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Master cylinders

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Old July 17th 08, 10:58 PM posted to rec.aviation.homebuilt
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Default Master cylinders

On Thu, 17 Jul 2008, Stealth Pilot wrote:

but what of the corrosion to the polished face of the cylinder the
o-ring mates to?

Why do you think corrosion will be a problem in an airplane, when it's not
a problem in cars if the brake fluid is changed occasionally? DOT 3 brake
fluid has additives that deal with the water absorption, so corrosion is
only an issue if additives are overwhelmed because the brake fluid never
gets changed.

I'll have non corrosive over cheap any day.

As will we all, if that's the question. But the question at hand is
somewhat different -- VERY flammable vs. slightly flammable. The fluid
you use is VERY flammable, and has a very low flash point. That's your
choice, of course, but I'll go with the slightly flammable stuff with a
higher flash point.
Old July 18th 08, 02:32 PM posted to rec.aviation.homebuilt
Ernest Christley
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Orval Fairbairn wrote:

DOT 3 fluid is chemically geared to steel components -- not aluminum. It
is also incompatible with Buna-N O-rings.

Of course, O-rings are cheap. Just replace 'em.

How about silicone DOT-5? That does not attract water and is not

As a side note, I have not heard of brake fires in light aircraft,
almost all of which use Mil-5606.

Read a few posts up. I posted several links, including one incident that I know of personally. Ed helped me rebuild my
engine, so I know he actually exists.
Old July 22nd 08, 07:30 AM posted to rec.aviation.homebuilt
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Default Master cylinders

On Jul 12, 6:24*am, Stealth Pilot
On Fri, 11 Jul 2008 23:59:21 -0700 (PDT), wrote:
I have some Gerdes master cylinders that were given to me years ago
which I am just now planning on using. *Don't know much about them,
but was wondering if it wouldn't be prudent to have them be rebuilt
( overhauled ) before I use them, since they've been on the shelf for
so long. *Is it actually possible to have them be overhauled and would
it be cost effective to do so? *Thanks


Neal you have a gem there in your hands.they are one of the neatest
little pieces of aviation kit ever invented.

the aircraft brake fluid in them, the red stuff, is not hydroscopic so
it never absorbs moisture. the innards of your master cylinders should
be in absolutely pristine condition. they may need a flush out to
remove accumulated crap but the worst you should find is worn o-rings.

in each side of your brake system there are 3 o-rings. 2 in the master
cylinder and 1 in the wheel puck.
the master cylinder has a feature known as a free piston. this piston
has one o-ring that makes the side seal. in the face of the pushrod is
another tiny o-ring that seals against the face of the free piston
when you apply toe brake to push the piston down.
these are the easiest things in the world to recondition if they are
old but in good nick.
buy the proper o-rings from your local aviation shop, my last ones
were under $aus20 for the 6 o-rings.

getting most of them apart involves taking the circlip out of the top.
this is a standard circlip and is about 3,000 times as stiff as it
needs to be. once you get that out without damaging anything the rest
is easy.
just slide it all apart. take the old o-rings out and put in the new
ones and your "reconditioning" is done. just remember to lube up the
new rings in brake fluid before putting them in position to prevent
nicking them.
reassemble, refill with red aviation brake fluid (actually an
automatic transmission fluid) and you will have pristine reconditioned
master cylinders.

you can find an exploded view of the innards of your cylinders in the
middle of an old cessna repair manual. in the 100 series cessna manual
it is figure 5-23 on page 5-37. it gives a perfect idea of how it all
goes together.

.....actually I'm lying. they've been on the shelf for so long now
they'll be totally stuffed. mate I'll take them off your hands for $15
and I'll pay the express postage :-) *:-) *:-)

Stealth (you have a gem there) Pilot

Thanks for the replies, guys. I was away from my computer for a few
days and actually had a chance to do some airplane building, so I
thought I'd jump at the chance. Not that I'm gullible or anything,
but I'm assuming I should keep these things and give them a shot. And
to think....I thought it was only British humor I didn't
"get." ( mate )

Old July 28th 08, 02:38 AM posted to rec.aviation.homebuilt
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Default Master cylinders

wrote in message
On Mon, 14 Jul 2008, Ernest Christley wrote:

Excellent post, Stealth, except avoid the red aviation fluid. Well, some
of the red aviation fluid. The stuff is fairly flammable.

What about using plain old DOT3 automotive brake fluid? It's cheap,
available everywhere, and non-flammable.

I do not recommend it. Ever, in an aircraft. Had a friend who used DOT3
fluid in his brakes. Worked fine until he actually used the brakes. He
tapped the brakes on landing. The brakes heated up inside those itty bitty
wheels we use on airplanes. The DOT3 fluid BOILED. Brakes locked up REAL
tight. Airplane went on its back. Made for some really expensive cheap
brake fluid.

Most aircraft brakes and hydraulic systems are made for 5606. Cherry juice.

Aircraft built prior to the end of WWII were probably NOT built for 5606.
In the thirties and early forties GA aircraft with hydraulic brakes ( there
weren't all that many of them ) use a mixture of glycerin and alcohol for
brake fluid. For those systems you can use a DOT fluid but NOT DOT3. Use
the silicone fluid. It costs about $20 a quart. It will not cause the
natural rubber parts in your brake system to melt like 5606 will! Been
there, had that done to me!

Highflight Aviation Services
Pinckneyville Airport ( PJY )

Old July 29th 08, 02:08 AM posted to rec.aviation.homebuilt
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Default Master cylinders

On Jul 15, 2:28 pm, wrote:

Well I guess that's the definitive answer. From now on it's DOT3 for my
bird's brakes, not that dangerous flammable stuff the spamcan drivers are
stuck with. The only potential downside I can see is water absorption,
which is more than handled by an annual flushing with a couple bucks'
worth of brake fluid.

And a few hundred bucks to fix the rubber bits. DOT-3 is a
vegetable-based fluid that is used with natural rubber. 5606 is a
mineral oil that is used with synthetic rubber. 5606 attacks natural
rubber, and DOT-3 attacks synthetic rubber. The flammability of 5606
is not an issue. I have no idea why anyone would risk trashing their
brakes and maybe the whole airplane when they either seize up or fail
altogether. The manufacturers of various vehicles specify certain
fluids for certain applications for very good reasons. A quart of 5606
would last the average owner about 10 years.
I spent 12 years building up and managing a machine shop that
rebuilt air brake equipment for trucks and earthmoving equipment and
hydraulic brake boosters for medium-duty trucks and some autos. We
made a LOT of money off people who put the wrong fluids in their brake
systems. We found motor oil (which is mineral oil) in systems designed
for DOT-3, and evidence of DOT-3 in air brake systems. Some of those
air brakes had alcohol injectors (for methyl hydrate) to prevent
freeze-up of the controls in cold weather (caused by condensation in
the compressed air) and guys would occasionally use anything handy
that had "alcohol" in it, like DOT-3 does. Wrong alcohol, though, and
boy, did it get expensive. The o-rings and other rubber bits would
swell and crumble and blow out and get into absolutely everything. If
you've had anything to do with modern air brake systems you'll realize
how extensive the damage can be. Those systems aren't simple.
Just drop some DOT-3 on your car's synthetic paint sometime and
see what happens.


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